Mid-lift is only available if you're using Jim Miller's rockers, it's a patented feature and does not exist unless you make it yourself. Setting the valve-side geometry to 1/2 up, 1/2 down @ 90 degrees just moves the error to the pushrod side. This is frequently an improvement, but that's all you can do - bump the discrepancy back & forth across the shaft axis.
We've talked about this before. Jim Miller's patent does not go on in perpetuity. It expired in 1994, and anyone who wishes to design a rocker with that concept, is free to do so. I have expanded on that concept, and that is what John (OP) has posted here. You are correct, though, that you won't find an off the shelf, single shaft rocker with the proper design.
